Lowestoft and Great Yarmouth regional Astronomers based in Lowestoft and Kessingland Astronomy group which is part of Lyra based in Kessingland

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Monday, 28 October 2013

SPA ENB No. 363

The SOCIETY for POPULAR ASTRONOMY

Electronic News Bulletin No. 363 2013 October 27

Here is the latest round-up of news from the Society for Popular Astronomy. The SPA is Britain's liveliest astronomical society, with members all over the world. We accept subscription payments online at our secure site and can take credit and debit cards. You can join or renew via a secure server or just see how much we have to offer by visiting http://www.popastro.com/

COMET ISON APPEARS INTACT NASA

A new image of the incoming Comet ISON suggests that the comet is intact, despite some suggestions that the supposedly fragile icy nucleus might disintegrate as the Sun warms it. The warmth that it has received so far, however, is nothing to what it will get when it passes closest to the Sun on November 28. In a Hubble image taken on October 9, the comet's solid nucleus is unresolved. The coma surrounding it is symmetrical and smooth, which it probably wouldn't be if the nucleus were in a number of separate pieces. A jet of dust that was seen in April is no longer visible. The comet will be closest to the Earth on December 26, at a distance of 40 million miles.

'PEBBLE' THOUGHT TO BE COMET FRAGMENT Witwatersrand University

A team of South African scientists and international collaborators believes that it has identified a small piece of rock as being formerly part of a comet that entered the atmosphere above Egypt about 28 million years ago. It exploded, melting some of the sand beneath it and forming a huge amount of yellow silica glass which lies scattered over a 6,000-square-km area of the Sahara. A magnificent specimen of the glass, polished by ancient jewellers, exists in Tutankhamun's brooch with its striking yellow-brown scarab. The impact of part of the comet also produced microscopic diamonds. Diamonds are produced from carbon-bearing material by high pressures, such as occur deep in the Earth but can also be generated by shock. Part of the comet reached the ground, and the shock of the impact produced the diamonds.

The team's attention was attracted to a black pebble found years ago by an Egyptian geologist in the area of the silica glass. Chemical analysis of the pebble led them to the conclusion that it is the first recognized hand specimen of a comet nucleus, rather than simply an unusual type of meteorite. Comet fragments have not been found on the Earth before, except as microscopic dust particles in the upper atmosphere and in Antarctic ice. Space agencies have spent large sums to secure very small amounts of pristine comet matter.

A new measurement of Mars' atmosphere by the Curiosity rover provides the best evidence yet that certain meteorites that have been believed to have come from Mars really did originate there, while at the same time it provides a way to rule out Martian origins of other meteorites. The rover measured the isotopic composition of argon. Isotopes of argon with masses of 36 and 38 exist naturally throughout the Solar System, but on Mars their relative abundance is altered because a lot of the planet's original atmosphere was lost into space, with the lighter form being lost more readily because it requires less energy to escape. Past analyses by Earth-bound scientists of gas bubbles trapped inside supposed Martian meteorites had already narrowed the Martian argon ratio to between 3.6 and 4.5 (that is 3.6 to 4.5 atoms of argon-36 to every one argon-38), giving a supposed Martian atmospheric value near four. Measurements by the Viking landers in the 1970s put the Martian ratio in the range four to seven; the new measurement gives 4.2.

One of the reasons that scientists have been so interested in the argon ratio in Martian meteorites is that it was -- before Curiosity -- the best measure of how much atmosphere Mars has lost since the wetter, warmer days billions of years ago. Had Mars held onto its entire atmosphere and its original argon, the isotopic ratio would be the same as that of the Sun and Jupiter, whose gravities are too high to allow argon to escape, so their argon ratio (5.5) represents that of the primordial Solar System. While argon comprises only a tiny fraction of the gases lost to space from Mars, it is special because it is a 'noble' gas, i.e. inert, not reacting with other elements or compounds, and therefore a straightforward tracer of the history of the Martian atmosphere. Other isotopes measured by Curiosity also support the idea of loss of atmosphere, but none so directly as argon.

WATER DISCOVERED IN REMNANTS OF EXTRASOLAR PLANET University of Warwick

Astrophysicists have found the first evidence of a water-rich rocky planetary body outside our Solar System in its shattered remains orbiting the white-dwarf star GD 61, 170 light years away. Using observations obtained with the Hubble telescope and the Keck telescope in Hawaii, they found an excess of oxygen -- a chemical signature that they interpreted as implying that the debris had once been part of a bigger body originally consisting of 26% water by mass. By contrast, only approximately 0.023% of the Earth's mass is water. Evidence for water outside the Solar System has previously been found in the atmospheres of gas giants and in radio-astronomical observations of gaseous material. The new study marks the first time that it has been attributed to a rocky body outside the Solar System, but that is not surprising, because we have not known even of the existence of such bodies until quite recently. Ice is widespread in the Solar System: the dwarf planet Ceres, and certain satellites of the major planets, contain ice buried beneath an outer crust, and analogous discoveries have recently been reported in such unlikely bodies as the Moon and Mercury. Some scientists believe that bodies like Ceres were the source of the bulk of terrestrial water. The researchers suggest that the water detected around the white dwarf GD 61 may have come from a planet that once orbited that star before it became a white dwarf. Like Ceres, the water was most likely in the form of ice below the planet's surface. From the amount of rock and water detected in the outer envelope of the white dwarf, the researchers estimate that the disrupted planetary body had a diameter of at least 90 km.

However, because their observations can only detect what is being accreted in recent history, the estimate of its mass is on the conservative side. It is likely that the object was as large as Vesta, one of the largest minor planets. Originally GD 61 was a star somewhat bigger than the Sun, and host to a planetary system. About 200 million years ago, GD 61 completed its evolution and became a white dwarf, yet parts of its planetary system survived. The water-rich minor planet entered an orbit that took it very close to the star, where it was disrupted by the star's gravity. The researchers believe that de-stabilising the orbit of the minor planet requires a so-far-unseen, much larger planet in orbit around the white dwarf. At this stage, all that remains of the rocky body is simply dust and debris in orbit around the white dwarf. In the remnants lie chemical clues which are said to point towards a previous existence as a water-rich terrestrial body.

ONE OF THE LARGEST STARS KNOWN IS TEARING ITSELF APART RAS

Stars with masses tens of times larger than that of the Sun have very short and dramatic lives compared to those of less-massive ones. Some of the most massive stars have lifetimes of less than a few million years before they exhaust their nuclear fuel and explode as supernovae. At the very ends of their lives they become unstable and eject a lot of material from their outer envelopes. That material has been enriched with heavy elements by nuclear reactions in the interior, and includes many of the elements that form rocky planets like ours, such as silicon and magnesium. How the material is ejected and how the loss affects the evolution of the stars is however still unknown.

Using the Very Large Telescope Survey Telescope (VST) at the Paranal Observatory in Chile an international team of astronomers has been surveying the Galaxy with a special filter to detect nebulae of ionized hydrogen. Meanwhile the VST Photometric H-Alpha Survey (VPHAS) has been searching the Galaxy for ejected material from evolved stars. Both observed the star cluster Westerlund 1, which is a massive cluster of several hundred thousand stars about five kiloparsecs away in the southern constellation Ara, but our view of it is so hampered by gas and dust that it appears comparatively dim in visible light. One of the stars, known as W26, in Westerlund 1 was observed to be surrounded by a cloud of glowing hydrogen. Such clouds glow because they are ionized, meaning that the electrons have been stripped away from the hydrogen atoms. Clouds of that type are not normally found around red supergiant stars such as W26; indeed, this is the first ionized nebula ever discovered around such a star. W26 itself is too cool to ionize the gas; the astronomers speculate that the source of the ionizing radiation may be either hot blue stars elsewhere in the cluster, or possibly a fainter, but much hotter, companion star to W26.

W26 is one of the largest stars ever recognized, with a radius 1500 times that of the Sun, and is also one of the most luminous red supergiants known. Such large and luminous massive stars are highly evolved, so W26 must 'soon' come to the end of its 'life' and explode as a supernova. The nebula observed around W26 is very similar to the one surrounding SN 1987A, the remnant of a star that exploded as a supernova in 1987. SN 1987A was the closest observed supernova to the Earth since 1604, and gave astronomers a chance to study the properties of such explosions. Studying objects like the nebula around W26 may help astronomers to understand the mass-loss processes that affect massive stars and lead up to their explosive demise.

MOST DISTANT GRAVITATIONAL LENS HELPS WEIGH GALAXIES ESA

An international team of astronomers has found the most distant gravitational lens yet -- a galaxy that, as predicted by Einstein's general theory of relativity, deflects and intensifies the light of an even more distant object. The discovery provides an opportunity to determine the mass of a distant galaxy. Since the first find in 1979, numerous such gravitational lenses have been discovered. In addition to providing tests of Einstein's theory, gravitational lenses have proved to be valuable tools. Notably, they enable us to determine the mass of the matter that is bending the light -- including the mass of the still-enigmatic 'dark matter'. The lens also magnifies the background light source, acting as a natural telescope that gives astronomers a more detailed look at distant galaxies than is otherwise possible.

Gravitational lensing involves two objects: one is further away and supplies the light, and the other is the lensing mass or gravitational lens, which sits between us and the distant light source, and whose gravity deflects the light. When the observer, the lens, and the distant light source are precisely aligned, the observer sees an Einstein ring -- a perfect circle of light that is the projected and greatly magnified image of the distant light source.

The recent discovery was made completely by chance. It looked like an extremely young galaxy, but it seemed to be at a much larger distance than expected. The Hubble telescope showed it to be an almost perfect Einstein ring, indicating a gravitational lens with very precise alignment of the lens and the background light source. The lensing mass is so distant that the light, after deflection, has travelled 9.4 billion years to reach us. Not only is this a new record, the object also serves an important purpose: the amount of distortion caused by the lensing galaxy allows a direct measurement of its mass. That provides an independent check on astronomers' usual method of estimating distant galaxy masses -- which rely on extrapolation from 'nearby' ones. Happily, the 'usual methods' pass the test.

Bulletin compiled by Clive Down

(c) 2013 the Society for Popular Astronomy

Society for Popular Astronomy

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Good Clear Skies--Astrocomet--Colin James Watling

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Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman) --

--Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork) --Information

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Astrocomet

I started in Astronomy in 1997 when the Comet Hale Bopp got me interested in Astronomy and Skywatching, since then I have joined Lyra and have vastly improved my knowledge of this very rewarding science.